Please change the subnet to a valid one for you. In the real world you would definitely *not* hardcode a subnet like this. But I wanted to keep this example very simple. Don’t know what subnet to use? Navigate your aws dashboard over to “VPC” and dig around.

Also of course edit for your key.

Ok, you’re ready to test. Let’s first ask terraform what it will do with the “plan” command:

levanter:terraform sean$ terraform plan
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but
will not be persisted to local or remote state storage.
The Terraform execution plan has been generated and is shown below.
Resources are shown in alphabetical order for quick scanning. Green resources
will be created (or destroyed and then created if an existing resource
exists), yellow resources are being changed in-place, and red resources
will be destroyed. Cyan entries are data sources to be read.
Note: You didn't specify an "-out" parameter to save this plan, so when
"apply" is called, Terraform can't guarantee this is what will execute.
+ aws_instance.example
ami: "ami-40d28157"
availability_zone: ""
ebs_block_device.#: ""
ephemeral_block_device.#: ""
instance_state: ""
instance_type: "t2.micro"
key_name: "seanKey"
network_interface_id: ""
placement_group: ""
private_dns: ""
private_ip: ""
public_dns: ""
public_ip: ""
root_block_device.#: ""
security_groups.#: ""
source_dest_check: "true"
subnet_id: "subnet-111ddaaa"
tenancy: ""
vpc_security_group_ids.#: ""
Plan: 1 to add, 0 to change, 0 to destroy.
levanter:terraform sean$

Conclusions

Terraform just supports JSON or it’s HCL (hashicorp configuration language). Actually the latter way of formatting is better supported.

On the CloudFormation side you can use yaml or json.

However CloudFormation can be clunky and frustrating to work with. For example to dry-run in terraform is easy. Just use “plan”. And isn’t something we’re going to do over and over?

In CloudFormation there is a “validate-template” option, but this just checks your JSON or YAML. It doesn’t hit amazon’s API or test things in any real way. They have added something called Change Sets, but I haven’t tried them too much yet.

Also CloudFormations error messages are really lacking. They often give you a syntax error or tell you a resource is incomplete without real details on where or how. It makes debugging slow and tedious. Sometimes I see errors at create-stack calls. Other times that succeeds only to find errors within the CloudFormation dashboard.